<style>
  body { overflow-x: scroll }
  div {
    width: 10px;
    height: 10px;
    background-color: #d64203;
  }
</style>

<body>
  <div style="width: 50px"></div> <!-- Unaffected by scrollbars. -->
  <div id="b"></div>
  <div style="width: 35px"></div> <!-- Unaffected by scrollbars. -->
  <div id="d"></div>

  <!-- Deliberately make scrollbars appear. -->
  <div style="width: 500px; height: 500px; background-color: black">
</body>

<script>
  // client{Width, Height} consist of the area _inside_ the scrollbars, so these
  // manually calculated units reflect the fact that with 'overflow: scroll' set,
  // viewport units are sized taking the scrollbars into account. Since we're
  // only dealing with 'overflow-x' here, only the height units are affected.
  var vh = 0.01 * document.body.clientHeight;
  document.getElementById('b').style.height = (25 * vh) + "px";
  document.getElementById('d').style.height = (25 * vh) + "px";
</script>
